/*
 * Copyright 2011-2013 Blender Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "stdosl.h"
#include "node_color.h"

float sky_angle_between(float thetav, float phiv, float theta, float phi)
{
  float cospsi = sin(thetav) * sin(theta) * cos(phi - phiv) + cos(thetav) * cos(theta);

  if (cospsi > 1.0)
    return 0.0;
  if (cospsi < -1.0)
    return M_PI;

  return acos(cospsi);
}

vector sky_spherical_coordinates(vector dir)
{
  return vector(acos(dir[2]), atan2(dir[0], dir[1]), 0);
}

/* Preetham */
float sky_perez_function(float lam[9], float theta, float gamma)
{
  float ctheta = cos(theta);
  float cgamma = cos(gamma);

  return (1.0 + lam[0] * exp(lam[1] / ctheta)) *
         (1.0 + lam[2] * exp(lam[3] * gamma) + lam[4] * cgamma * cgamma);
}

color sky_radiance_old(normal dir,
                       float sunphi,
                       float suntheta,
                       color radiance,
                       float config_x[9],
                       float config_y[9],
                       float config_z[9])
{
  /* convert vector to spherical coordinates */
  vector spherical = sky_spherical_coordinates(dir);
  float theta = spherical[0];
  float phi = spherical[1];

  /* angle between sun direction and dir */
  float gamma = sky_angle_between(theta, phi, suntheta, sunphi);

  /* clamp theta to horizon */
  theta = min(theta, M_PI_2 - 0.001);

  /* compute xyY color space values */
  float x = radiance[1] * sky_perez_function(config_y, theta, gamma);
  float y = radiance[2] * sky_perez_function(config_z, theta, gamma);
  float Y = radiance[0] * sky_perez_function(config_x, theta, gamma);

  /* convert to RGB */
  color xyz = xyY_to_xyz(x, y, Y);
  return xyz_to_rgb(xyz[0], xyz[1], xyz[2]);
}

/* Hosek / Wilkie */
float sky_radiance_internal(float config[9], float theta, float gamma)
{
  float ctheta = cos(theta);
  float cgamma = cos(gamma);

  float expM = exp(config[4] * gamma);
  float rayM = cgamma * cgamma;
  float mieM = (1.0 + rayM) / pow((1.0 + config[8] * config[8] - 2.0 * config[8] * cgamma), 1.5);
  float zenith = sqrt(ctheta);

  return (1.0 + config[0] * exp(config[1] / (ctheta + 0.01))) *
         (config[2] + config[3] * expM + config[5] * rayM + config[6] * mieM + config[7] * zenith);
}

color sky_radiance_new(normal dir,
                       float sunphi,
                       float suntheta,
                       color radiance,
                       float config_x[9],
                       float config_y[9],
                       float config_z[9])
{
  /* convert vector to spherical coordinates */
  vector spherical = sky_spherical_coordinates(dir);
  float theta = spherical[0];
  float phi = spherical[1];

  /* angle between sun direction and dir */
  float gamma = sky_angle_between(theta, phi, suntheta, sunphi);

  /* clamp theta to horizon */
  theta = min(theta, M_PI_2 - 0.001);

  /* compute xyz color space values */
  float x = sky_radiance_internal(config_x, theta, gamma) * radiance[0];
  float y = sky_radiance_internal(config_y, theta, gamma) * radiance[1];
  float z = sky_radiance_internal(config_z, theta, gamma) * radiance[2];

  /* convert to RGB and adjust strength */
  return xyz_to_rgb(x, y, z) * (M_2PI / 683);
}

shader node_sky_texture(int use_mapping = 0,
                        matrix mapping = matrix(0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0),
                        vector Vector = P,
                        string type = "hosek_wilkie",
                        float theta = 0.0,
                        float phi = 0.0,
                        color radiance = color(0.0, 0.0, 0.0),
                        float config_x[9] = {0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
                        float config_y[9] = {0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
                        float config_z[9] = {0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0},
                        output color Color = color(0.0, 0.0, 0.0))
{
  vector p = Vector;

  if (use_mapping)
    p = transform(mapping, p);

  if (type == "hosek_wilkie")
    Color = sky_radiance_new(p, phi, theta, radiance, config_x, config_y, config_z);
  else
    Color = sky_radiance_old(p, phi, theta, radiance, config_x, config_y, config_z);
}
